diff --git a/cmd/sdrd/main.go b/cmd/sdrd/main.go
index 6832e9b..40fb7f9 100644
--- a/cmd/sdrd/main.go
+++ b/cmd/sdrd/main.go
@@ -449,6 +449,7 @@ func runDSP(ctx context.Context, srcMgr *sourceManager, cfg config.Config, det *
 	dcBlocker := dsp.NewDCBlocker(0.995)
 	dcEnabled := cfg.DCBlock
 	iqEnabled := cfg.IQBalance
+	plan := fftutil.NewCmplxPlan(cfg.FFTSize)
 	useGPU := cfg.UseGPUFFT
 	var gpuEngine *gpufft.Engine
 	if useGPU && gpuState != nil && gpuState.Available {
@@ -480,6 +481,7 @@ func runDSP(ctx context.Context, srcMgr *sourceManager, cfg config.Config, det *
 			}
 			if upd.window != nil {
 				window = upd.window
+				plan = fftutil.NewCmplxPlan(cfg.FFTSize)
 			}
 			dcEnabled = upd.dcBlock
 			iqEnabled = upd.iqBalance
@@ -546,7 +548,7 @@ func runDSP(ctx context.Context, srcMgr *sourceManager, cfg config.Config, det *
 					spectrum = fftutil.SpectrumFromFFT(out)
 				}
 			} else {
-				spectrum = fftutil.Spectrum(iq, window)
+				spectrum = fftutil.SpectrumWithPlan(iq, window, plan)
 			}
 			now := time.Now()
 			finished, signals := det.Process(now, spectrum, cfg.CenterHz)
diff --git a/internal/fft/fft.go b/internal/fft/fft.go
index 36ab34c..33b6700 100644
--- a/internal/fft/fft.go
+++ b/internal/fft/fft.go
@@ -1,10 +1,6 @@
 package fftutil
 
-import (
-	"math"
-
-	"gonum.org/v1/gonum/dsp/fourier"
-)
+import "math"
 
 func Hann(n int) []float64 {
 	w := make([]float64, n)
@@ -21,6 +17,11 @@ func Hann(n int) []float64 {
 }
 
 func Spectrum(iq []complex64, window []float64) []float64 {
+	plan := NewCmplxPlan(len(iq))
+	return SpectrumWithPlan(iq, window, plan)
+}
+
+func SpectrumWithPlan(iq []complex64, window []float64, plan *CmplxPlan) []float64 {
 	n := len(iq)
 	if n == 0 {
 		return nil
@@ -34,9 +35,12 @@ func Spectrum(iq []complex64, window []float64) []float64 {
 		}
 		in[i] = complex(float64(real(v))*w, float64(imag(v))*w)
 	}
-	fft := fourier.NewCmplxFFT(n)
 	out := make([]complex128, n)
-	fft.Coefficients(out, in)
+	if plan != nil && plan.N() == n {
+		plan.FFT(out, in)
+	} else {
+		NewCmplxPlan(n).FFT(out, in)
+	}
 
 	power := make([]float64, n)
 	eps := 1e-12
diff --git a/internal/fft/plan.go b/internal/fft/plan.go
new file mode 100644
index 0000000..c6ae297
--- /dev/null
+++ b/internal/fft/plan.go
@@ -0,0 +1,24 @@
+package fftutil
+
+import "gonum.org/v1/gonum/dsp/fourier"
+
+type CmplxPlan struct {
+	fft *fourier.CmplxFFT
+	n   int
+}
+
+func NewCmplxPlan(n int) *CmplxPlan {
+	if n <= 0 {
+		return &CmplxPlan{}
+	}
+	return &CmplxPlan{fft: fourier.NewCmplxFFT(n), n: n}
+}
+
+func (p *CmplxPlan) N() int { return p.n }
+
+func (p *CmplxPlan) FFT(out, in []complex128) {
+	if p == nil || p.fft == nil {
+		return
+	}
+	p.fft.Coefficients(out, in)
+}
diff --git a/internal/sdrplay/sdrplay.go b/internal/sdrplay/sdrplay.go
index 13f69e2..dcccc2d 100644
--- a/internal/sdrplay/sdrplay.go
+++ b/internal/sdrplay/sdrplay.go
@@ -128,6 +128,7 @@ func (s *Source) configure(sampleRate int, centerHz float64, gainDb float64, bwK
 	if err := cErr(C.sdrplay_api_LockDeviceApi()); err != nil {
 		return fmt.Errorf("sdrplay_api_LockDeviceApi: %w", err)
 	}
+	defer func() { _ = cErr(C.sdrplay_api_UnlockDeviceApi()) }()
 
 	var numDevs C.uint
 	var devices [8]C.sdrplay_api_DeviceT
@@ -139,10 +140,8 @@ func (s *Source) configure(sampleRate int, centerHz float64, gainDb float64, bwK
 	}
 	s.dev = devices[0]
 	if err := cErr(C.sdrplay_api_SelectDevice(&s.dev)); err != nil {
-		_ = cErr(C.sdrplay_api_UnlockDeviceApi())
 		return fmt.Errorf("sdrplay_api_SelectDevice: %w", err)
 	}
-	_ = cErr(C.sdrplay_api_UnlockDeviceApi())
 
 	var params *C.sdrplay_api_DeviceParamsT
 	if err := cErr(C.sdrplay_api_GetDeviceParams(s.dev.dev, &params)); err != nil {